This Post Has Been Edited by the Author
In Reply to: RE: Lux posted by bcherry on October 04, 2007 at 01:38:49
I am quite busy on other things, but I'll try "putting out the fire with gasoline" (David Bowie - Cat People).
For a long time I have been in two minds about Penthode drivers and High Mu, low output Impedance Triode drivers. I always liked both, but for different reasons and which was the "right" one dependend upon context, but invariably what one gained over the other in one area, it lost elsewhere. Brians summary is concise and good, it always a choice of compromise, depending on many factors.
The topology used in the Lux, which was BTB originally dubbed "Bushido" by me (in both a transparent pun and as program - Brian suggested it was "counterpunnable") aims at bridging the gap.
The "reactive interstage" part between output stage and driver acts basically as "turbo charger", producing the more graceful overload and quicker, much easier overload behaviour of a gridchoke (or interstage transformer) loaded triode driver and then some, but without the interstage transformers often way too obvious bandwidth limitations and even better drive and overload recovery/overdrivability as triode & gridchoke.
Loading the cathode follower with a choke removes almost all of the objectionable sonic charateristics of a cathode followe (I hasten to add loading with a nice CCS does so too, but requires an extra negative supply of a good few volts AND chokes still sound a little more organic) and is nowadays easy to do, with a proliferation in available loading chokes (back when I did most of my work on SE Amp's the only choice was Tango TC-160-15 and importing these from Japan made some expensive interstages look like a good choice, gridchokes where also basically nada).
The actual voltage gain and thus the whole harmonic behaviour comes from the pPntode driver stage, which Yamamoto San has championed for many years (even though only his most recent and somewhat cut down products achieved significant recognition, like the A-08 Amp driven by a WE 717), as well as Jean Hiraga and many others (I'll happily add my voice to this chorus).
So, bottom line, if you want the macrodynamic abilities and easy overdrive of the Triode & Interstage Transformer or Gridchoke drive combined with the finesse, delicacy and tonal colours of a 91 (or my earlier C3m/EL84 Legacy), have your cake AND eat it.
There will be cases where the Lux will be possibly even marginally worse than a LD91+, on detail retrieval and delicacy (only VERY MARGINALLY though), I would put these cases in the use of 103db/W/m or above efficient speakers (and we talk real not paper efficiency which cuts numbers right down and readly excludes most Lowthers, all Tannoys and Altec Coaxial and anything from Fostex's full range series) in normal sized rooms, where you rarely exceed the first watt.
So all of you with Avant Garde's, Beauhorn Virtuosos, Klipschorns or Oris Horns (et al) and LD91's can sleep well, the rest, well, if you never play Mahler, Ravel/Mussorsky, LedZed, Bela Fleck or Moloko and similar SPL intensive stuff, sleep well too, the rest I suggest may face sleepless nights. If the speaker is more like a real 95db/W/m (or lower) case AND you like to handle things more complex than "Girl and Guitar" I would now recommend the Lux, basically cojones like the Castro Brothers, giving the one fingered victory salute to the worlds richest and most powerfull nation for almost five decades!
I hope that puts things into context and I actually would consider the Lux still "two stage" in terms of gain structure.
Now, how can I get Brian to make a version that has old WE Style socktes for both the input and interstage position AND 10V heater windings, so I can make one with a 310A Gainstage and a 311B Interstage (plus 274A rectifiers and real 300B's o course, me being a bit snobbish)?
Kind regards Thorsten
PS, for a lovely CD, try "Iz - Facing Future", not neccesarily audiophile and some tracks have some major mike overload, but boy has this guy a voice, awsome!
Edits: 10/06/07Follow Ups: